Bars based on synthetic surfactant (“syndet” bars) and having some fatty acid soap are known. Syndet bars have levels of synthetic surfactant well beyond those of the invention.
Fatty acid soap bars containing some synthetic surfactant are also known in the art. Such bars may contain free fatty acid (superfat), although generally (though not necessarily) not at levels where free fatty acid (FFA) level is greater than that of soap. The art fails to disclose that in bars with high fatty acid/soap, low synthetic, the total level of unsaturated soap can be no more than a defined amount.
When additional free fatty acid is added to either fatty acid soap or synthetic soap bars, this additional free fatty acid is known as “superfat”. It is generally added to provide benefits such as a richer, creamier lather. The well known Dove® bar, for example, contains about 20% free fatty acid. Dove® has levels of synthetic far higher than levels used in the subject invention.
Generally, it is important to limit the upper level of free fatty acid (FFA) used in a bar for a variety of reasons. For example, since FFA is hydrophobic, use of high amounts would be expected to decrease the ability of a bar to foam or lather.
Unexpectedly, applicants have found that when FFA acid is added in much greater amounts (in one embodiment of the invention it is added to the bar composition using an under-neutralization process as disclosed herein), the bar will still retain excellent foaming properties. While not wishing to be bound by theory, this is believed to occur because the acid-soap microstructure of the bar which develops (for example, due to underneutralization when this process is used) has enough integrity to be initially extruded, but that integrity wears away upon washing efficiently enough to provide sufficient lather (i.e., from the soap/free fatty acid), even though minimal amounts of surfactant are used. That is, it is believed that an acid-soap complex initially acts as a structurant (which does not defoam) and that as the structure breaks down, it allows good lathering during the wash process. At the same time, since it is acting as a structuring complex, far less synthetic is needed (e.g., for foaming) than might previously have been believed.
The bars thus comprises a minimum of about 65% of a combination of fatty acid soap and FFA; less than about 25% (preferably, at least about 10%) synthetic surfactant and from 1 to about 15%, preferably 2 to 14% (less than 15%) water. In a preferred embodiment, the level of FFA is equal to or more preferably greater than the level of soap. Preferred levels of free fatty acid is greater than about 40% by weight. The bars are generally, although not necessarily (e.g., may be melt cast or frame cooling process) prepared by an extrusion process and the bar will lather at least 50 ml using standard bar appraisal technique or BLAM.
As noted, high levels of free fatty acid (e.g., above about 35%, preferably above 40%) are preferred as is ratio of FFA to soap of 1:1 or preferably higher. Further, levels of synthetic are low. Dove® bars contain about 20% FFA and much higher levels of synthetic. In our invention, the level of FFA is also preferably higher than the level of synthetic used. Also in our invention, the level of water should be higher than 5% by weight but lower than about 14% by weight, preferably less than about 12% by weight.
U.S. Pat. No. 3,989,647 to Prince discloses bars containing up to about 35% by wt. fatty acid and at least 40% non-soap surfactant. The bars of the subject invention generally contain above about 35% FFA and also contain much lower levels of synthetic (i.e., below about 25% by wt.).
U.S. Pat. No. 4,673,525 to Small et al. discloses bars containing 20-70%, preferably 40-70% synthetic surfactant, up to 40% “moisturizer” (which is preferably not fatty acid) and up to 25% soap. The ratio of synthetic to soap is 2:1 to 12:1. In the subject application, the level of soap generally exceeds the level of synthetic and the synthetic to soap ratio never approaches 2:1.
U.S. Pat. No. 4,695,395 to Caswell discloses bars comprising soap, sodium isethionate, FFA and acyl isethionate. The amount of FFA is up to 25% (see claim 3). Levels of FFA in the subject invention are higher.
U.S. Pat. No. 4,832,861 to Resch discloses bars which may comprise 30 to 70% soap and 1 to 40% FFA (e.g., stearic acid). From the examples, it is clear the bars are predominantly soap bars with cocoyl isethionate and relatively smaller amounts of FFA. The subject invention comprises much higher FFA. Further, the subject application requires hardness of extruded bar of at least 90, preferably at least 100 kPa as measured by cheese wire method and it is not clear that bars of Resch would need such limitation. Indeed, given high levels of salt used in Resch, it may well be that many of the bars would likely not be this hard.
U.S. Pat. No. 5,225,097 to Kacher et al. discloses skin pH freezer bars requiring at least 15% water.
U.S. Pat. No. 5,661,120 to Finucane discloses bars with up to 35% FFA and up to 25% soap. The subject invention requires at least 65% combination soap and 6 FFA.
U.S. Pat. No. 6,218,348 to Aronson discloses bars comprising fatty acid soap, up to 35% FFA, polyalkylene glycol of defined MW and salts of protic acid. From the specification and claims, it is clear the reference is concerned with bars that are predominantly (preferably 50-75% by wt.) fatty acid soap and lower amounts (preferably 2 to 14%) FFA.
Other patents of general interest include the following:                U.S. Pat. No. 3,991,001 to Srinivasan et al.;        U.S. Pat. No. 4,812,253 to Small et al.;        U.S. Pat. No. 4,954,281 to Resch;        U.S. Pat. No. 5,006,529 to Resch;        U.S. Pat. No. 5,076,953 to Jordan et al.;        U.S. Pat. No. 5,204,014 to Redd et al.;        U.S. Pat. No. 5,225,098 to Kacher et al.;        U.S. Pat. No. 5,543,072 to Fost et al.;        U.S. Pat. No. 5,681,980 to Beerse et al.;        U.S. Pat. No. 5,945,389 to Richard et al.;        U.S. Pat. No. 6,069,121 to Cassady et al.; and        U.S. Pat. No. 6,242,394 to Chambers et al.        
In none of the patents of which applicants are aware is there disclosed bars where the level of FFA exceeds the level of soap; the level of syndet is below a certain level (below 25% but preferably at least 10% by wt.); and there is found an acid-soap complex. Specifically, the fatty acid and soap together comprise at least about 65%, preferably at least 66%, more preferably at least 68%, more preferably at least 70% of the bar and FFA is at least 35%, preferably at least 36%, more preferably at least 38% of bar, most preferably at least 40% and even more preferably above 40% by weight. Further, synthetic surfactant comprises less than about 25%, preferably less than about 23%, more preferably less than about 20% of composition and water comprises less than about 15%, preferably less than about 13%. The bars of the invention are preferably prepared by under-neutralizing free fatty acid during formation of an acid-soap complex.